The invention relates to a laser leveling instrument having a beam platform that can be leveled and fine self-leveling of the laser beam, having an inner cylinder which is oscillatingly suspended in an outer cylinder and which carries orientation elements.
Laser leveling instruments are known in a multiplicity of designs. They serve either for the generation of a laser beam oriented perpendicularly to the vertical or for the generation of a horizontal reference plane with the aid of a laser beam rotating about the vertical direction. Within this context, the beam platform is understood to be a mounting surface of the laser leveling instrument, which mounting surface can be leveled manually with a limited degree of accuracy and on which mounting surface the means deflecting the laser beam into the horizontal are disposed.
Usually, the laser is incorporated into the laser leveling instrument in such a way that its optical axis extends in the vertical direction. The deflection into the horizontal takes place by means of mirrors or prisms, in particular by means of rotatably mounted pentaprisms. The mounting surface for the deflecting elements is, in accordance with the above definition, the beam platform.
In the case of known laser leveling instruments, this beam platform is fixedly connected to the housing of the system. For coarse leveling, the housing has adjusting feet and bubble levelers.
An arrangement for automatic coarse leveling is also known, in which the laser leveling instrument is disposed on an electromechanical stand. The legs of the stand are altered in their height by means of spindles, until such time as this procedure is terminated by mercury switches at the leveling instrument housing, which function as inclination sensors. The coarse leveling takes place with a degree of accuracy of approximately 50" and is relatively slow.
Where the accuracy requirements are more stringent, a fine leveling takes place by means of a compensator. In this case, an optomechanical compensation using lenses which are displaceable relative to one another has in particular become well established. One of the lenses is incorporated in a cylindrical tube, fixedly within the system, and the other is suspended on metal filaments, in oscillating fashion in the tube. When an instrument has been adjusted, the beam emitted by the laser extends in the optical axis of the fixedly incorporated lens and is diverted by the oscillating lens in such a way that it falls, in a vertical direction, onto the deflecting element. Where semiconductor lasers are used, the lenses are also responsible for the beam collimation. In this case, it is also possible to suspend the entire lens combination in oscillating fashion, as can be seen from DE-OS 2 944 408 to which reference is made hereinbelow.
The oscillatingly suspended lens can cooperate with three light barriers fitted to the housing. The light barrier signals can drive light emitting diodes, which are fitted in star shaped fashion to the instrument housing and thus provide the user with a correlation for the adjustment of the foot screws for coarse leveling. They replace the otherwise usual circular levels. It has also been proposed to use the signals for the adjustment of the abovementioned electromechanical stand. To this end, however, the light barriers must be oriented in aligned fashion in relation to the legs of the stand.
The range of compensation is limited by the space available within the compensator tube. During the measurement, the oscillatingly suspended lens must not touch the internal surface of the tube. Accordingly, the abovementioned light barriers serve in particular also to monitor the free oscillatory suspension. An interruption of the light barrier beam with a drop in level to a predetermined threshold leads to a denergization of the laser diode. Only after repeated coarse leveling can the system be operated again.
The oscillating lens can also swing so strongly, by reason of vibrations, that it interrupts the light barrier. In order to avoid this, a magnetic damping is provided, which compels a rapid decay of the oscillatory swing. The damping operates in the manner of an eddy current brake. In this case, it has to be ensured, by careful selection of materials and design, that magnetic forces do not influence the vertical orientation of the oscillation in the neutral position.
A summary representation of the abovementioned prior art is found in the dissertation by H. Wuller, D 82 Diss. T H Aachen, (1988), ISSN 0515-0574, development and investigation of a rotary leveling instrument and of a photoelectric leveling staff for the automation of the geometric leveling element.
DE-OS 2 944 408 discloses a pendulum compensator in which an oscillatingly suspended inner cylinder swings with the compensation lenses in an outer cylinder. The cylinders are relatively long and have a small intermediate space. In the event of alteration of the spacing of the cylinder surfaces, air is displaced, which, by reason of the flow resistance, generates a damping of the oscillatory swing.
The outer cylinder is electrically insulated with respect to the housing. In the event of contact of the inner cylinder with the outer cylinder, a wire is grounded and the laser diode is immediately deenergized thereby. To recommence operation, it is necessary to carry out a repeated coarse leveling with the use of level indicators; this restores the pendulum to its working range.
In place of compensation lenses it is also possible to fit the laser diode to the pendulum.